The present invention relates to an anisotropically electroconductive adhesive or, more particularly, to an electroconductive adhesive suitable for adhesively bonding two electric circuit boards with heating under pressure and capable of imparting electroconductivity between the circuit boards in a direction perpendicular to the plane of the circuit boards.
Various types of electroconductive adhesives are known in the prior art which can be used for adhesively bonding two electric circuit boards along with establishment of electroconductivity therebetween including those prepared by dispersing a large amount of electroconductive particles in a matrix of a synthetic polymeric material such as thermoplastic resinous and rubbery materials based on polyurethane, polyester, synthetic rubber and the like and thermosetting resinous materials based on epoxy, silicone and the like. A problem in the above mentioned thermoplastics-based electroconductive adhesives is the disadvantage of the increase in the electric resistance and decrease in the adhesive bonding strength between the bonded circuit boards when they are under a high-temperature or high-humidity condition due to the weakened contact between the conductive particles and terminals with decreased in the retentive power of the matrix polymer. The thermosetting resin-based conductive adhesives have different problems. When the adhesive is of the two-package type, i.e. of the type formulated and packaged in two packages containing each different component or components from the other to be mixed together directly before use, the workability of the adhesive is not always satisfactory because of the relatively short pot life of a ready-mixed composition. When the adhesive is of the one-package type, i.e. of the type storable as ready-mixed, the pot-life is also not so long to cause gradual viscosity increase so that difficulties are sometimes encountered in the exact oontrol of the working conditions with poor productivity in mass production and the problem of the increase in the electric resistance and decrease in the adhesive bonding strength can also not be avoided.